KR100784338B1 - Manufacturing method for low refractive index thin film and antireflection coating method using it - Google Patents

Abstract

The present invention provides a method for producing an optical thin film having a very low refractive index and very small anisotropy using a porous thin film microstructure, and a method for producing a low refractive index thin film having excellent antireflection coating having excellent transmission characteristics in a wide wavelength range and a large angle of incidence. It provides an anti-reflective coating method used.

The low refractive index thin film used in the antireflective coating of the present invention is a layer including the porous dielectric thin film deposited using the gradient incidence deposition method and has an optically isotropic property, and the refractive index of the thin film is changed by adjusting the inclined incidence angle. In addition, by using a dielectric layer having a lower refractive index than the substrate in the antireflective coating, it is characterized in that the antireflective coating having a small reflection for a large wavelength range and a large angle of incidence with a small number of layers. Since the refractive index can be adjusted by adjusting the inclination angle of the substrate during deposition, the existing chamber structure can be used as it is, and only one type of material can be used to prevent contamination in the chamber. Not only is this possible, it is possible to improve productivity by simplifying thickness errors and processes.

Porous, low refractive index thin film, antireflective coating, MgF2, SiO2

Description

Low refractive index thin film manufacturing method and anti-reflective coating method using the same {MANUFACTURING METHOD FOR LOW REFRACTIVE INDEX THIN FILM AND ANTIREFLECTION COATING METHOD USING IT}

1 is a schematic system configuration diagram for implementing a general electron beam deposition method.

Figure 2 is a cross-sectional SEM image of the MgF2 thin film deposited by a general electron beam deposition method (α = 0 degrees).

3 is a surface SEM image of a MgF2 thin film deposited by a general electron beam evaporation method (α = 0 degrees).

4 is a schematic system configuration diagram for implementing a general gradient incidence deposition method.

FIG. 5 is a cross-sectional SEM image of an MgF2 thin film deposited by a gradient incidence deposition method (α = 80 degrees). FIG.

6 is a surface SEM image of an MgF2 thin film deposited by a gradient incidence deposition method (α = 80 degrees).

7 is a graph showing the refractive index of the MgF2 thin film according to the oblique incidence angle.

FIG. 8 is a graph of reflectivity of MgF2 single layer antireflective coating deposited by gradient incidence deposition (α = 0 degrees and α = 80 degrees).

9 is a graph showing the results of phase difference measurement of an MgF2 thin film deposited by a gradient incidence deposition method (α = 0 degrees and α = 80 degrees).

 10 is a cross-sectional SEM image of the deposited MgF2 thin film rotated at 3 rpm with an inclination angle α = 80 degrees.

Figure 11 is a surface SEM image of the deposited MgF2 thin film rotated at an angle of inclination α = 80 degrees 3rpm.

FIG. 12 is a graph illustrating a phase difference measurement result of a SiO 2 thin film deposited by fixing and rotating a substrate at an inclination angle α = 80 degrees by a gradient incidence deposition method. FIG.

Figure 13 schematically shows a thin film structure for a wide band antireflective coating according to the present invention.

FIG. 14 is a graph of reflectance at vertical incidence of an antireflective coating having a two-layer structure using MgF 2; FIG.

FIG. 15 is a graph of reflectance according to vertical incidence (AOI = 0 degrees) and incident angle (AOI = 40 degrees) of a two-layer antireflective coating using MgF2.

16 is a graph of reflectance according to the thickness (5%) and refractive index (2%) error of the antireflective coating of the two-layer structure using MgF2.

17 is an admittance graph of an antireflective coating having a two layer structure using MgF2.

18 is a graph of reflectance measurement results of an antireflective coating having a two-layer structure using MgF2.

19 is a graph of reflectance of an antireflective coating having a three layer structure using MgF2.

20 is a reflectance graph of the antireflective coating in the UV region of a two layer structure using SiO 2.

<Description of the symbols for the main parts of the drawings>

1: container 2,6,8,9,10: thin film

3-a, 3-b, 7 4: substrate 4: shutter

5: physical thickness measuring device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-reflective coating technique used in various optical elements such as prisms, optical filters, optical systems for displays, optical thin films for optical communications, UV exposure apparatuses, and the like. The present invention relates to a method for producing a low refractive index thin film having very low refractive index and optically isotropic optical properties, and a method of antireflective coating having a small number of layers and excellent transmission characteristics over a wide wavelength range and a large angle of incidence. .

Antireflection coating is an optical thin film coating method to increase the light transmittance from the substrate. It is a method of reducing the reflection at the interface caused by the difference between the refractive index of the substrate and the refractive index of air by using the interference effect of light. Widely used in

If the admittance in the medium and the final admittance in the thin film are the same in the optical film, then there is an antireflective coating with a reflectance R of R = 0 and no reflected light. Therefore, a thin film having a multi-layered thin film structure is generally deposited on a substrate, and the reflectance is lowered by adjusting the refractive index, the thickness, and the number of layers so that the admittance of the air and the admittance of the thin film are almost the same (HA Macleod, Thin-Film Optical Filters, 3rd ed. 2001). As the antireflective coating method, the following methods are used.

1. Single layer antireflective coating

In general, the reflectivity of glass having a refractive index of 1.5 in air is about 4%, and the refractive index ( n _f ) of the thin film must satisfy the following equation in order to coat one layer on the glass substrate so that the reflectance is zero.

n ² _f = n _sub n _air

Where n _f is the refractive index of the thin film, n _sub is the refractive index of glass ( n _sub = 1.5) and n _air is the refractive index of _air ( n _air = 1.0). At this time, the thickness of the thin film is 1/4 wavelength optical thickness.

Therefore, when the refractive index n _f of the thin film satisfying the antireflective coating is obtained as one layer, n _f = 1.22. However, since a thin film having such a low refractive index does not exist, MgF 2 ( n _f = 1.38) or SiO 2 ( n _f = 1.46), which is a low refractive index material, is mainly used. In this case, since the refractive index of the thin film is not 1.22, which is a refractive index that satisfies the antireflective coating, there is a disadvantage in that the reflectance is not reduced much.

In order to solve this problem, most antireflective coatings use a multilayer structure of two or more layers instead of one layer.

2. Two layer antireflective coating

In order to solve the problem of one layer of anti-reflective coating, the two-layer antireflective coating is a method of making the admittance of the thin film close to the admittance of air (1.0) by using a high refractive index material and a low refractive index material. In general, however, a two-layer antireflective coating can result in an almost R = 0 reflectance at the reference wavelength, but a V-type antireflective coating with high reflectivity at other wavelengths. Therefore, a method of extending the antireflective coating band by using another layer of 1/2 wavelength optical thickness is used.

This structure has the effect of widening the narrow anti-reflective area of the V-type, resulting in a W-shaped anti-reflective coating. All of the above antireflective coating structures are constituted by thin films having a quarter wavelength optical thickness or a half wavelength optical thickness with respect to a reference wavelength.

However, there is a material limitation for such an antireflective coating, so it is difficult to obtain antireflection by only 1/4 or 1/2 wavelength optical thickness alone. Therefore, the anti-reflective coating is made of a multilayer structure consisting of layers of thin films, not 1/4 or 1/2 optical thicknesses.

3. Multilayer antireflective coating

For antireflective coatings having a low reflectance and a wide range of antireflective wavelengths, a multi-layer antireflective coating can generally be achieved by using two or three or more materials as high and low refractive index materials.

US 3,185,020 has a three-layer antireflective coating using three kinds of materials on a substrate (1.45-1.75). Deposition first deposits a thin film of intermediate refractive index (1.8-1.85) with a quarter wavelength optical thickness. A thin film of high refractive index (1.9-2.3) is deposited with a 1/2 wavelength optical thickness and a low refractive index (1.38) thin film is deposited with a 1/4 wavelength optical thickness in the last layer.

US Pat. No. 3,960,441 replaces an intermediate layer with a thin film having a non-uniform refractive index (Gradient Refractive Index) whose refractive index is continuously changed in the thickness direction in a three-layer antireflective coating using thin films having uniform refractive indices, thereby minimizing reflection at the interface and non-reflecting The anti-reflective coating is realized by using a structure that widens the area.

US Pat. No. 4,372,987, US Pat. No. 3,604,784 is an antireflective coating using a method of controlling the refractive index of a thin film by mixing two metal oxides (Al2O3 + TiO2, Al2O3 + Ta2O5) in an antireflective coating composed of a multilayer thin film. In particular, in the case of the antireflective coating having a three-layer structure, the intermediate layer is mixed with two metal oxides (Al 2 O 3 + TiO 2 and Al 2 O 3 + Ta 2 O 5) to maintain a constant reflectance in the reflection region.

US Pat. No. 5,170,291 uses a thin film having three refractive indices to realize an antireflective coating in a wide area through an antireflective coating having a four-layer structure.

In addition, the methods in US Pat. No. 5,450,238 (four-layer structure), US Pat. No. 5,194,990 (three-layer structure) and the like can form an antireflective coating using three or more layers of structures and two or more kinds of materials.

The conventional antireflective coating methods described above should be deposited using at least two different materials, and in particular, a multi-layered structure having three or more layers should be used for the antireflective coating in a wide area.

Scott R. Kennedy and Michael J. Brett "Porous broadband antireflection coating by glancing angle deposition" Applied optics 42, 2003, 4573-4579 used porosity using a gradient angle deposition to continuously change the refractive index on the glass substrate. Depositing a SiO 2 thin film having a structure enables one layer of antireflective coating having a low reflectance in a wide region of 400 nm to 1000 nm. However, this method not only has to continuously adjust the angle of incidence during deposition, but also has the trouble of continuously adjusting the thickness according to the angle.

Meanwhile, in Gisia Beydaghyan, Kate Kaminska, Tim Brown, and Kevin Robbie, "Enhanced birefringence in vacuum evaporated silicon thin films" Applied optics 43, 2004, 5343-5349 With this increase (20 ° to 85 °), the refractive index decreased from about 4.3 to 1.3. In addition, anisotropy was shown to be greatest when the oblique incident angle was about 60 degrees.

The deposition using the oblique incidence deposition method used Oblique Deposition (Oblique Deposition) for the orientation of the color display liquid crystal panel in US Patent 4,490,015, US Patent 6,426,786 B1, US Patent 6,867,837, etc., SiO2, SiO, CeO2, Al2O3, MgF2, Metal oxides such as CaF2 and LiF and metal fluorides are used to direct the surface, and in Korean Patent Publication 1998-084672, birefringence is generated by depositing a dielectric using a gradient incident deposition method to have a specific growth direction. The method of manufacturing a polarizing element is used.

The inclined incidence deposition method mainly uses SiO 2, TiO 2, Y 2 O 3, Ta 2 O 5, Bi 2 O 3, Nb 2 O 5, SiO, ZnS, CeO 2, MoO 3, SnO 2, to produce a birefringent plate using anisotropy of a thin film as in US Pat. No. 4,874,664. High refractive index materials, such as WO3, are deposited at large incidence angles using an electron beam and used for the production of birefringent plates and the like.

Such oblique incidence deposition is described by K. Robbi, L.J. Friedrich, and S. K. Dew, "Fabrication of thin films with highly porous microstructures" J. Vac. Sci. Technol. A 13 (3) 1995 with K. Robbie and M. J. Brett, "Sculptured thin films and glancing angle deposition: Growth mechanics and applications" J. Vac. Sci. Technol. A 13 (3), 1997, etc., explain the principle of thin film growth and column structure, and describe how to control the thin film column structure.

As the inclined incident angle increases, the thin film deposited by the oblique incidence deposition method is grown into a thin film having a porous structure by the shadow effect of the thin film micropillar (HA Macleod, Thin-Film Optical Filters, 3rd ed. 2001). .

Therefore, when the oblique incidence angle is largely deposited, the porosity of the thin film is increased by the column structure and the shadow effect, and the effective refractive index of the thin film is lowered. However, there is a problem in that optically anisotropy characteristics appear due to the pillar microstructure of the thin film. This is a problem that it is difficult to apply to a general optical coating having an optically isotropic (Isotropic) characteristics.

In the case of the conventional antireflective coating method, at least one or more low refractive index layers are necessarily required, and at this time, there is a limit to the type of material used for depositing the low refractive index layer having a low refractive index.

In addition, the conventional method requires a multilayer structure because it is difficult to have an antireflection coating having excellent permeability in a wide area with only one layer, and two or more kinds of materials should be used. In addition, in the case of the antireflective coating in which the two materials are mixed and deposited so that the refractive index is continuously changed, it is difficult to control the mixing ratio of the materials during the deposition process.

In the case of one layer of anti-reflective coating using a non-uniform thin film to have a continuous refractive index, there is a problem that it is necessary to continuously change the angle of incidence during deposition and to perform the cumbersome adjustment of the angle of incidence and precise thickness control.

In addition, in the case of the oblique incidence deposition method, although the effective refractive index is lowered, the optical anisotropy increases as the inclined incidence angle increases, which makes it difficult to apply to an antireflective coating that should be optically isotropic.

Accordingly, the present invention has been made in view of the problems of the prior art, and an object of the present invention is to fabricate an optical thin film having a low refractive index and very small optically anisotropy using a porous thin film microstructure, and having a wide wavelength range and a large angle of incidence. The present invention provides a low refractive index thin film manufacturing method capable of excellent antireflection coating and an antireflection coating method using the same.

The low refractive index thin film manufacturing method according to the present invention for achieving the object of the present invention, to obtain a low refractive index thin film having a porous structure by depositing a dielectric material, such as a metal oxide or metal fluoride on the substrate by a gradient incident deposition method. It features.

The low refractive index thin film is a material having an absorption of 0.01 or less in a wavelength range to be used, and uses a metal oxide such as SiO2, Al2O3, HfO2, Y2O3, or a metal fluoride such as MgF2, CaF2, LaF3, Na3AlF6, and the low refractive index thin film. Silver is deposited at an oblique incidence angle of 40 degrees or more, and the low refractive index thin film is a porous thin film having a columnar microstructure, and at a predetermined oblique incidence angle α to deposit a layer having very low refractive index, uniform thickness, and very low anisotropy. The substrate is fixed and deposited while rotating the substrate by 360 degrees, or deposited in a zigzag structure of + α and -α.

In the anti-reflective coating method of the present invention for achieving the above object, a low refractive index thin film layer having a porous structure having a lower refractive index than the substrate by depositing a dielectric material such as a metal oxide or a metal fluoride at an angle of inclination of more than 40 degrees on a substrate To obtain the antireflection property by using at least one layer of the thin film layer.

In addition, the anti-reflective coating method of the present invention for achieving the above object, by depositing a dielectric material such as a metal oxide or a metal fluoride by a gradient incident deposition method on the substrate to form a low refractive index thin film layer having a porous structure having a lower refractive index than the substrate The optical characteristics are obtained by alternately laminating a thin film having a high refractive index and the like deposited with the thin film layer in a general manner.

In addition, the anti-reflective coating method of the present invention for achieving the above object, by depositing a dielectric material such as a metal oxide or a metal fluoride by a gradient incidence deposition method using only one type, these thin film layers at least two layers or more Deposition in a multi-layered structure, characterized in that the deposition while changing the inclined incidence angle differently for each layer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following examples are merely to illustrate the present invention is not limited to the contents of the present invention.

1 shows a schematic system configuration for implementing a general electron beam deposition method, in which a substrate 3a is mounted in a high vacuum state and a material contained in a container 1 containing a material using an electron beam (not shown). Is heated to evaporate to deposit the thin film 2, and the substrate 3-a is a transparent substrate such as an organic substrate.

The chamber is provided with a vacuum pump (not shown) for maintaining a high vacuum and an MFC (not shown) for supplying gas (Ar, O 2, etc.) from the outside into the chamber. In order to measure the thickness, the physical thickness measuring apparatus 5 is positioned near the substrate 3-a and the shutter 4 is positioned on the container 1 containing the material to adjust the thickness of the thin film 2.

Referring to the method of manufacturing a thin film using the vacuum equipment as shown in Figure 1 as follows.

First, the substrate 3-a is mounted in a holder (not shown) and the material to be deposited is filled in the container 1 containing the material, and then a high vacuum state of about 10 ^-6 torr is introduced into the chamber using a vacuum pump. To be At this time, the temperature of the substrate 3-a may be heated to about 200 to 300 degrees.

In the deposition method of the thin film, the electron beam is first used to melt the material contained in the container 1 and then the shutter 4 is opened so that the evaporated material is deposited on the substrate 3-a. In this case, as shown in FIG. 1, the evaporated particles are deposited in a direction substantially perpendicular to the deposition surface of the substrate 3-a. At this time, the substrate 3-a may be rotated to make the thickness of the thin film 2 uniform on the substrate 3-a.

In general, the thermal evaporation method using an electron beam has a low energy of about 0.1 eV, and the mobility is small, so that the thin film grows on the substrate and grows in the shape of a column. As the pillar grows, the shadow effect obscured by the pillar decreases the probability that particles arriving behind fill the void. Therefore, during the growth of the thin film has a columnar microstructure (Columnar Microstructure) including the thin film pillar and the void space.

2 and 3 show examples of the cross section and the surface of the MgF2 thin film deposited by the above method. FIG. 2 shows that the thin film has a uniform columnar structure perpendicular to the deposition surface, and FIG. 3 shows that the cross section and the surface have a dense structure.

Figure 4 shows a schematic system configuration for implementing a general oblique incidence deposition method, which is also a basic system for implementing the present invention.

This allows the holder to be tilted at an angle α in the same vacuum deposition chamber structure as in FIG. 1. The method of depositing a thin film by an oblique incidence deposition method is performed in the same manner as the general deposition method described above, and as shown in FIG. 4, the evaporation direction of the evaporated particles is at an angle with respect to the deposition surface of the substrate 3-b. It is a method to be deposited in a maintained state. At this time, in order to make the thickness of the thin film 6 uniform, the holder of the substrate 3-b may be rotated or may be moved in a zigzag of + α and -α.

The actual cross-sectional and surface images of the MgF2 thin film deposited by the above method are shown in FIGS. 5 and 6. When the deposition direction of the evaporated particles is deposited at an angle of α = 80 degrees, the thin film 6 is grown by inclining the deposition surface of the substrate 3-b and having a pillar microstructure as shown in FIG. 5.

In addition, an empty space is created by the thin-film pillar microstructure, which shows a porous structure. On the surface of the thin film 6, many empty spaces are observed as shown in FIG. 6, and have a porous structure in which empty spaces are formed along the column.

7 shows the refractive index at 550 nm according to the inclined incidence angle of the MgF2 thin film deposited by the inclined incidence deposition method.

When the oblique incidence angle is α = 0 degrees, the refractive index of the MgF2 thin film has a value of about 1.38. As the oblique incidence angle increases, the refractive index of the MgF2 thin film becomes porous. The antireflective coating has a refractive index of about 1.20.

In FIG. 8, the reflectances of the one-layer antireflective coating in which the oblique incidence angles were deposited on α = 0 degrees and α = 80 degrees on a glass substrate having a refractive index of 1.52 were compared. At this time, the thickness of the thin film was deposited with a 1/4 wavelength optical thickness at 550nm.

Compared with the conventional anti-reflective coating (n = 1.38) deposited by the conventional method (?? = 0 degrees), the one-layer anti-reflective coating (n = 1.20) deposited with an oblique incidence angle of α = 80 degrees has a reflectance near R = 0. It is lowered and shows a wider area of antireflection.

These results show that the low refractive index dielectric thin film having a porous structure can be deposited by controlling the inclination angle when the dielectric thin film is deposited using the electron beam.

In general, thin films deposited using the inclined incidence deposition method have an effective refractive index, but anisotropy increases due to the porous pillar microstructure of the film (Gisia Beydaghyan, Kate Kaminska, Tim Brown, and Kevin Robbie). , "Enhanced birefringence in vacuum evaporated silicon thin films" Applied optics 43, 2004, 5343-5349).

Such anisotropic properties are difficult to use in optical filters or antireflective coatings that must exhibit optically isotropic properties. This anisotropy is caused by the column microstructure, and because the column microstructure composed of the pillar and the void does not have an isotropic structure, it is caused by the difference in refractive index between the pillar and the void.

Therefore, as a method of depositing a thin film having low anisotropy, a material having a low refractive index such as MgF2 (n = 1.38) is deposited. In this case, since the refractive index (1.38) of the material is small from the refractive index (1.0) of the air, The refractive index difference by columnar microstructure can be made small. Another method is to rotate the substrate while maintaining the inclination angle α such that the column microstructure is isotropic.

FIG. 9 shows the birefringence measurement results of the MgF2 single-layer thin film deposited at an angle of incidence angle α = 0 degrees and α = 80 degrees (FIGS. 2 and 5). The retardation of the MgF2 thin films deposited at the incidence angles of inclination of α = 0 and α = 80 degrees, respectively, is very small, indicating that they have almost isotropic optical properties.

FIG. 10 is a cross-sectional view of the deposited thin film by rotating the MgF2 thin film by rotating it at 3 rpm while depositing an oblique incident angle α = 80 degrees, and has a pillar structure of the thin film, and has a porous structure with many void spaces inside the thin film. Is showing.

In addition, Figure 11 is a surface image of a thin film deposited by the above method shows that the thin film has a porous structure on the surface. The thin film deposited in this manner exhibits almost isotropic optical properties, and the thin film deposited by rotating and fixing the SiO 2 (1.46) thin film having a refractive index larger than MgF 2 (n = 1.38) in FIG. Phase difference measurements are shown. When the thin film was deposited without rotating, the anisotropy was increased and Δn had a value of 0.022. However, when the substrate was rotated, the anisotropic characteristic was greatly decreased to 0.005. This shows that it is effective to rotate the substrate to reduce the anisotropy of the thin film deposited by the oblique incidence deposition method.

Therefore, by increasing the inclination angle of the substrate to increase the porosity of the thin film can be deposited a thin film having a low refractive index, the method of rotating and depositing the substrate can reduce the anisotropy of the material with a high refractive index and at the same time deposit a uniform thickness Show how you can.

FIG. 13 shows a schematic view of a coating structure capable of obtaining antireflection in a wide wavelength region using a low refractive index thin film deposited using the above method.

When using a low refractive index layer deposited using a dielectric material such as metal oxide or metal fluoride with an inclination angle of α above 40 degrees for antireflective coating, at least one layer can be used to obtain antireflective characteristics. Increasing the number of layers in a 2-3 layer structure as shown in FIG. 13 allows the wavelength region to be antireflected to be widened.

_A structure using a thin film deposited on the glass substrate 7 using a material having a low refractive index and having an oblique incidence angle of α _A , α _{B, and} α _C is deposited. In the structure of the antireflective coating, the inclined incidence angles of the respective layers are deposited in order of α _A , α _{B, and} α _C from the substrate 7 side, and the inclined incidence angles are α _A <α _B <α _C. The refractive index of each thin film at this time is n _A > n _B > n _C and the layer 8 on the substrate 7 has the largest refractive index n _A , and the layer 10 on the air side has the smallest refractive index n _C. Each optical thin film has a 1/4 wavelength optical thickness, and the remaining layers except for the last layer 10 may be deposited as one layer by removing intermediate layers in consideration of reflectance and wavelength region, or insert new layers in the middle. . In this case, the material to be deposited is a dielectric material such as metal oxide or metal fluoride, which is deposited by a gradient incidence deposition method to deposit a thin film having a lower refractive index than the substrate 7, and is deposited using only one type of material.

When the deposition method is performed using the above-described method and structure, it is advantageous to prevent contamination in the chamber because it is deposited using one material, and the tilt angle of incidence angle α may be in the range of 0 to 85 degrees by tilting the substrate holder during deposition. As it is deposited by giving 1 ~ 3 steps, the manufacturing process is relatively simple compared to the conventional deposition method.

In addition, the antireflective coating having such a structure uses only one material (MgF2), and uses only layers having a lower refractive index than the substrate, so that the antireflective coating can be made in a large area even with a small number of layers. Also, the change in reflectance is small, and can exhibit anti-reflective characteristics even at a large incident angle. In addition, the antireflective coating deposited in this manner can reduce the total thickness and the number of layers compared to the conventional coating.

The refractive index of the MgF2 thin film having a refractive index of 1.52 at 550 nm and an oblique incidence angle of α = 0 and α = 80 degrees is 1.38 and 1.20, respectively, so that only one material (MgF2) is used for the structure (Fig. 13). The reflectance in the case of the two-layer structure using) is shown in FIG. In the broad wavelength range from 400nm to 1200nm, the reflectance is less than 1%.

FIG. 15 shows a wide range of 400 nm to 1000 nm even when an incident angle of light in the air is incident at a large angle of 40 degrees as a result of calculating the reflectance of light incident at an incident angle of the incident beam having a vertical incidence angle and having an inclination angle of 40 degrees. It is shown that there is an antireflective coating having a reflectance of 1% or less in the wavelength region.

16 shows the sensitivity to thickness and refractive index of the antireflective coating. This shows the change in reflectivity when the error of the thickness is 5% and the error of the refractive index is 2%, and shows that the antireflective property is maintained even when the thin film is deposited with the above error. This has the advantage of allowing large process errors in the anti-reflective coating.

 The reason why the two-layer wide anti-reflective coating is possible is that only the material having a lower refractive index than the substrate is used in the anti-reflective coating, and the structure can be described as an admittance in FIG. 17. In order for the reflectance of the thin film to be zero, the admittance of the thin film may be (1,0), which is the admittance of air. Starting with (1.52,0), the admittance of the substrate, the admittance becomes (1.26,0) in a circle while the first thin film is deposited. In this case, when the thickness of the thin film is 1/4 wavelength, a semicircle that meets the real axis is drawn.

However, the limit of the refractive index limits the size of the admittance trajectory. Therefore, in the second layer, when a material having a lower refractive index is deposited than the first layer, an admittance trajectory is drawn to the left by the difference in reflectance.

Therefore, the reflectance becomes lower because the air is closer to the refractive index (1,0). At this time, since the trajectory of the admittance is a circle, the admittance of the antireflective coating using only a layer having a refractive index lower than that of the substrate is always smaller than or equal to the substrate.

Therefore, an antireflection coating using only a low refractive index thin film having a smaller refractive index than a substrate can obtain a coating having a smaller influence on reflectance against changes in thickness, refractive index, and angle of incidence than when a material having a larger refractive index is used than a substrate. The advantage is that an antireflective coating having a very small number of layers and having a very large antireflection area can be provided.

FIG. 18 shows measurement results of an antireflective coating having a two-layer structure using only one material (MgF 2). In the broad wavelength range of 400 nm to 1300 nm, an antireflective coating having an average reflectance of 0.4% is shown. In order to further lower the reflectance, only one material (MgF2) can be used for the antireflective coating in a three layer structure, and FIG. 19 shows the reflectance in the three layer structure. In the case of the three-layer structure, the reflectance is lower than that of the two-layer antireflective coating, and the optical characteristics can be obtained even in the non-reflective area.

In the case of the antireflection coating using the above method, a metal oxide such as SiO 2, Al 2 O 3, HfO 2, Y 2 O 3, and metal fluorides such as MgF 2, CaF 2, LaF 3, and Na 3 AlF 6 may be used to deposit a thin film smaller than the refractive index of the substrate.

At this time, since SiO2 and most metal fluorides are transparent in the UV (ultraviolet) region, there is an advantage that an antireflective coating for UV is possible. Since quartz (Quartz), which is a transparent substrate in the UV region, has a refractive index of about 1.51 at 245 nm, when depositing a SiO2 thin film using the above method, a thin film having a refractive index of 1.20 can be deposited by adjusting the incident angle. In the case of one layer of antireflective coating having a structure of 13 (when one layer having a refractive index of 1.2 is used), the reflectance can be lower than that of the conventional single layer antireflective coating using MgF 2 (refractive index of 1.38).

As shown in FIG. 20, in the case of a two-layer antireflective coating using a layer having a refractive index of 1.48 and a layer having a thickness of 1.20 using SiO 2, the reflectance was 0.3% in a wide wavelength range (200 nm to 300 nm) using only one material (SiO 2). The following anti-reflective coating can be performed.

The present invention has a reflectance of 1.0% or less in the VIS (visible light) region and the IR (infrared) region, and the non-reflective wavelength region is 300 nm or more.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art various modifications of the present invention without departing from the spirit and scope of the invention described in the claims below Or it may be modified.

As described above, the present invention has the following effects.

First, since the refractive index can be adjusted by adjusting the inclination angle of the substrate during deposition, the existing chamber structure can be used as it is.

Second, because only one type of material is used, contamination in the chamber can be prevented.

Third, wide range of anti-reflective coating is possible with only two layers, which can improve productivity by simplifying thickness error and process.

Fourth, since a very low refractive index (1.0 <n <1.38) and an almost isotropic optical thin film can be obtained compared to the refractive index obtained by the conventional method, the optical properties of the optical multilayer thin film can be improved and the number of layers of the thin film can be reduced.

Fifth, in the case of using a metal fluoride-based material such as MgF2, CaF2, LaF3, there is an advantage that can be used for the anti-reflective coating in this region because there is almost no absorption in the UV region.

Sixth, it can be applied to the ultraviolet region, visible light region and near infrared region, and has a wide anti-reflective region, so that it can be applied to various optical elements, thereby replacing the existing anti-reflective coating.

Claims (24)

In the method of manufacturing a low refractive index thin film having a porous structure by depositing a deposition material on a glass substrate by a gradient incident deposition method, Fixing the glass substrate at a first inclined angle of incidence, depositing a first low refractive index thin film layer in a zigzag structure by depositing a material having the same or lower refractive index as the glass substrate while rotating the glass substrate by 360 degrees; The glass substrate is fixed at a second oblique incidence angle greater than the first oblique incidence angle, and a material having the same or lower refractive index as that of the glass substrate is deposited while rotating the glass substrate by 360 degrees on the first low refractive index thin film layer in a zigzag structure. Depositing a second low refractive index thin film layer Low refractive index thin film manufacturing method comprising a. The method of claim 1, The low refractive index thin film manufacturing method, The glass substrate is fixed to a third inclined incidence angle greater than the second inclined incidence angle, and a material having the same or lower refractive index as that of the glass substrate is deposited while rotating the glass substrate by 360 degrees on the second low refractive index thin film layer in a zigzag structure. Depositing a third low refractive index thin film layer Low refractive index thin film manufacturing method characterized in that it further comprises. The method according to claim 1 or 2, The material having a lower refractive index than the glass substrate is a method of manufacturing a low refractive index thin film, characterized in that the metal oxide or metal fluoride. The method of claim 3, wherein The metal oxide is a low refractive index thin film manufacturing method, characterized in that any one of SiO2, Al2O3, HfO2, Y2O3. The method of claim 3, wherein The metal fluoride is MgF2, CaF2, LaF3, Na3AlF6, characterized in that any one of low refractive index thin film manufacturing method. The method of claim 1, The first inclined incident angle is a low refractive index thin film manufacturing method, characterized in that more than 0 degrees. The method of claim 1, The second inclined incident angle is greater than the first inclined incident angle, characterized in that the low refractive index thin film, characterized in that less than 85 degrees. The method of claim 2, And the third inclined angle of incidence is greater than the second inclined angle of incidence and is less than or equal to 85 degrees. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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